Maintaining ribbon tension with tapered-shunt reed switch control apparatus

ABSTRACT

Apparatus for maintaining tension in a ribbon which is being wound on an intermittently driven take-up spool. A reed switch having a tapered shunt is used to control a motor which drives the take-up spool. The motor is driven intermittently to maintain the ribbon tension substantially constant within predetermined limits.

United States Patent [1 Berry 1 Mar. 19, 1974 1 MAINTAINING RIBBONTENSION WITH TAPERED-SHUNT REED SWITCH CONTROL APPARATUS [75] Inventor:Jack Beer-y, Farmin gton, Mich.

[73] Assignee: Burroughs Corporation, Detroit,

Mich.

[22] Filed: Mar. 16, 1972 [21] Appl. No.: 235,362

Related U.S. Application Data [63] Continuation of Ser. No. 52,635. July6. 1970,

abandoned.

[52] US. Cl 242/75.43, 242/67.3 R, 242/193, 335/236 [51] Int. Cl. B65h77/00, B65h 17/02, G03b 1/04 [58] Field of Search 242/67.3 R. 75.43,75.5, 242/45, 67.1 R, 75.51, 75, 190, 193, 194;

[56] References Cited UNITED STATES PATENTS 3/1965 Jones 242/1903,164,696 1/1965 Pusch 335/205 X 265.485 10/1882 Cochran 335/2073.142.788 7/1964 Gelenius 335/236 3,426,976 2/1969 Maxey 242/75433.226.506 12/1965 Angrisand 335/205 1.952.196 3/1934 Coil 242/7543FOREIGN PATENTS OR APPLICATIONS 792,357 8/1968 Canada 335/237 PrimaryExaminer-John W. Huckert Assistant ExaminerEdward J. McCarthy Attorney,Agent, or Firm--Ralzemond B. Parker; Jerold I. Schneider; Edwin W. Uren{5 7] ABSTRACT Apparatus for maintaining tension in a ribbon which isbeing wound on an intermittently driven take-up spool. A reed switchhaving a tapered shunt is used to control a motor which drives thetake-up spool. The motor is driven intermittently to maintain the ribbontension substantially constant within predetermined limits.

8 Claims, 7 Drawing Figures PAIENTED MR 19 I974 SHEEY 1 0F 2 PATENTEI]MR 19 I974 SHEET 2 [1F 2 FIG.5

FIG

MAINTAINING RIBBON TENSION WITH TAPERED-S a REED SWITCH CONTROLAPPARATUS This is a continuation, of application Ser. No. 52,635, filedJuly 6, 1970, abandoned.

BACKGROUND OF THE INVENTION 1. Field of Invention This invention relatesgenerally to apparatus for unwinding and rewinding ribbon-like memberswhile maintaining substantially constant tension by intermittentlydriving a take-up spool under the control of a tapered shunt reedswitch. Although the invention is applicable to various web, strand,tape and ribbon-like members it has been found particularly useful inthe environment of magnetic ink ribbons as used in printing devices.Therefore, without limiting the meaning of the word ribbon, theinvention will be described in this environment. This invention may beutilized when the ribbon is used only once as well as when the ribbon isreusable and also may be utilized when separate supply and take-up reelsor spools are used as well as when the supply and take-up spools aremounted for rotation on a single shaft as in the preferred embodiment.Therefore the detailed description should be read as merely illustrativeof the principles of this invention.

2. Description of the Prior Art When ribbon is fed at a first rate to atake-up spool which is operating at a different or intermittent ratethere are, of course, repeated variations in the ribbon tension. Thesevariations may result in tangling, stretching, or breaking the ribbon.When ribbon having a magnetic oxide coating or an ink coating is used,such as in the tape recording and printing arts, excess stretching ofthe ribbon can cause fragments of the oxide coating or ink coating tobreak off thereby rendering corresponding portions of the ribbonuseless. Prior art solutions to these problems generally provideapparatus designed to maintain the torque developed by the take-up spooldrive motor within specific narrow limits that will not damage theribbon.

Such prior art solutions have utilized either complex circuitry toprovide the rapidly responsive take-up spool motor control that isrequired to restrict the torque, or more modest circuitry which resultsin a higher cyclic rate of take-up spool operation. The latter typecontrol results in shorter life for the various components.

SUMMARY OF THE INVENTION With these prior art problems in mind it is anobject of the present invention to provide means for simply andeconomically maintaining substantially uniform tension in a ribbon-likemember.

It is another object of the present invention to maintain ribbon tensionby means of a rapidly responsive control system.

It is yet another object of the present invention to maintain thetension in a ribbon substantially constant within predetermined limits.

It is a further object of the present invention to maintain tensionindependent of the torque characteristics of a take-up spool drive motorused for rewinding a ribbon and thus control the maximum diameter ofribbon on a rewind spool.

It is yet another object of the present invention to maximize the lifeof a reed switch that is effectively utilized for controlling a ribbontake-up spool drive motor such that substantially uniform tension in theribbon is maintained.

These and other objects are accomplished in an apparatus for maintainingtension in a ribbon which is being wound on an intermittently driventake-up spool. A reed switch having a tapered shunt is used to control amotor that drives the take-up spool; the motor being drivenintermittently to maintain the ribbon tension substantially constantwithin predetermined limits. The tapered shunt prevents an excessivelyrapid recycling of the reed switch, thereby preserving the useful lifeof the reed switch control.

BRIEF DESCRIPTION OF THE DRAWINGS The above objects of the presentinvention together with other objects and advantages which may beattained by its use will become apparent upon reading the description ofthe invention in conjunction with the following drawings. In thedrawings wherein like numerals designate corresponding parts:

FIG. 1 is a flow diagram of a ribbon transport system which incorporatesthe present invention;

FIG. 2 is an elevation view of the ribbon supply and take up structureof the present invention;

FIG. 3 is a sectional view taken along line 3-3 of FIG. 2 and includes aportion of the ribbon and utilization device;

FIG. 4 is a side elevation view of a collection line tension mechanism;

FIG. 5 is a plan view of FIG. 4 with various parts broken away;

FIG. 6 comprising FIG. 6A and FIG. 6B is an illustration for comparingoperational characteristics of different types of shunts; and

FIG. 7 is a side elevation of a ribbon level change device.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 illustrates the path thata ribbon 11 follows from a supply spool 13 through a drive andutilization apparatus to a take-up spool 15. More specifically theribbon 11 is assumed to follow a clockwise path from the supply spool 13through a supply tension apparatus 17, past a utilization device such asprinter 19, past a drive wheel or roller 21, through a collection ortakeup tension apparatus 23 and over a level changer 25 to take-up spool15. As the drive wheel or drive roller 21 pulls the ribbon from thesupply spool 13 through the printer it simultaneously supplies usedribbon to be rewound on the take-up spool 15; take-up spool 15 beingintermittently driven and the take-up tension apparatus 23 maintainingtension in the used ribbon as it is being rewound.

Referring to FIG. 2, a vertically disposed shaft 27 is housed within afreely rotatable sleeve 29. The shaft and sleeve are journaled in ahorizontally disposed frame 31. The supply spool 13 is locked onto thesleeve 29 at a first vertical level above the frame 31 and rotates withthe sleeve. In a preferred operation this first vertical levelcorresponds to that level at which the ribbon is utilized by theprinter. In a plane above the supply spool 13, the take-up spool 15 islocked into position on the shaft 27. Preferably the shaft has a slottherein and spool 15 has a key to engage the slot. In a conventionalfashion a motor (not shown) drives shaft 27 to rotate the upper ortake-up spool 15.

Referring now to FIGS. 2 and 3, the operation of the ribbon supplytension apparatus 17 will be explained. One end of a shaft 33 isjournaled in frame 31 and the shaft extends downward from the frame. Atriangular plate 35 is disposed below the upper part of the frame 31 andthe apex of this triangular plate is rotatably mounted on shaft 33. Apivotable protruding arm 37 is disposed above and pin connected to theright-hand portion of plate 35. A circular indentation 39 in theprotruding arm 37 has a radius of curvature equal to that of sleeve 29.The plate 35 is disposed to the left of shaft 27 such that indentation39 may engage sleeve 29. As the plate is rotated in a counterclockwisedirection around shaft 33 the indentation 39 engages sleeve 29 toprovide a friction brake for stopping the rotation of sleeve 29 andsupply spool 13. Arm 37 is urged into frictional engagement with sleeve29 by a spring 41.

Disposed below triangular plate 35 and also mounted on shaft 33 is alever 43. Lever 43 is biased or urged by spring 45 in a counterclockwisedirection about shaft 33. There is a generally arcuate slot 47 parallelto and adjacent to the base of triangular plate 35. A vertical stud 49on lever 43 extends upward through slot 47. The free rotational movementof lever 43 is accordingly limited by the engagement of stud 49 with theends of slot 47. Once lever 43 and stud 49 are rotated in either aclockwise or counterclockwise direction beyond the point at which thestud contacts a corresponding extremity of slot 47, the lever 43 and thetriangular plate 35 will thereafter rotate together as a result of suchcontact. It is apparent, however, that in the preferred embodiment onlyclockwise rotation of lever 43 and plate 35 simultaneously is ofparticular significance since the contact of the indentation 39 of theprotruding arm 37 with the sleeve 29 prevents significantcounterclockwise rotation of the triangular plate 35.

At the end of lever 43 opposite to the end mounted on shaft 33 is a pin51 which extends vertically upward to the level of the supply spool 13.A guide roller 53 is freely spindled on pin 51 at a level identical tothat of the supply spool 13. For convenience in illustration the guideroller is also shown in FIG. 1 however the designation 17 should bethought of as referring to the entire supply ribbon tension apparatusincluding roller 53.

Considering the operation of the supply tension apparatus generallydesignated at 17, as the ribbon 11 is fed into the utilization device orprinter 19, the pressure on the ribbon from the rotation of roller 21would be generally clockwise as seen in the view of FIG. 1. Thispressure would tend to move the roller 53 to the left causing agenerally clockwise rotation of lever 43 against the yielding force ofspring 45. When the ribbon tension from the printer exceeds the tensionlimit, which is defined as the stud 49 reaching one extremity of slot47, the braking effect of indentation 39 contacting sleeve 29 isreleased and new ribbon may be drawn from the supply spool 13. This newribbon would serve to decrease the tension in the ribbon between thearea of the ribbon supply spool 13 and the wheel 21; this decrease inribbon tension permits springs 41 and 45 to urge triangular plate 35 andlever 43, respectively, in a counterclockwise direction back into theirbiased positions. As this occurs, indentation 39 again engages and stopsthe rotation of sleeve 29 and supply spool 13.

This completes the intermittent ribbon feed or demand ribbon feed cycle.

As a precautionary measure a magnetic flux diverting member 55 may bemounted on the lever 43 between pin 51 and stud 49. This member 55diverts the magnetic flux from a reed switch 57 mounted on the brakesideof the plate 35 if the lever 43 rotates counterclockwise a predetermineddistance. The switch 57 is so positioned that this predeterminedrotation occurs only if no ribbon or a broken ribbon is loaded in thesystem or if the ribbon is not loaded past guide roller 53. If switch 57is opened by movement of the flux diverting member 55 the entire systemshould be shut down. Thus switch 57 could be located in the main powerline.

As illustrated in FIG. 1, the drive wheel 21 feeds used ribbon from theprinter 19 to the take-up spool 15 via the collection line or take-upline tension mechanism 23. As previously indicated, spool 15 is drivenpositively by the motor rotating shaft 27. As shown in greater detail inFIGS. 4 and 5, the tension mechanism 23 includes a horizontal frame 59of non-magnetic material such as aluminum which supports two spindles61, 61. A cylindrical guide roller 63, 63 is rotatably mounted on eachspindle. Disposed through and below the frame 59 in spaced relationshipare two vertical cylindrical posts 65, 65 each having a flat bottom thusgiving the posts the cross sectional shape of an inverted T. A shunt ofmagnetic material is slidably mounted on the posts 65, 65' in a planeparallel to and below the frame 59. This shunt includes an elongatedrectangular magnetic shunt portion 67, and, at one end, an annular shuntportion 69 of tapered width which gradually decreases as the distancefrom the rectangular portion thereof increases. The slidable mounting ofthe shunt is accomplished through two elongated slots 71, 71' formedtherein. The slots are arranged to permit the rectangular portion toslide along and rest on posts 65, 65'. Near the center of therectangular portion 67 of the shunt there is a vertically disposedspindle 73. The upper portion of the spindle 73 passes through a slot 75formed in the frame 59. A guide roller 77 is rotatably mounted on thespindle 73 above the frame 59 at the same vertical level as the fixedrollers 63 and 63' and the drive wheel 21 (FIG. 1). It is to be notedthat in the plan view of FIG. 5 the left slot 71, in the partiallybroken view, is below the level of frame 59, slot 75 in frame 59 isshown but right slot 71 is omitted for clarity. However, all three slotsare colinear in a plan view.

As the shunt slides in either direction along its elongated slots 71,71' the spindle 73 and the roller 77 are carried with it. A spring 79has one end attached to the lower extension of the spindle 73 and theother end attached to a portion of the frame. Spring 79 urges the shuntand roller 77 to the right as viewed in FIGS. 4 and 5 which is away fromthe tapered end 69 of the shunt. The urging of spring 79 is resisted bythe tension in the ribbon 11 against the slidable roller 77. If theseforces remained in a state of equilibrium the roller 77 would neverslide but would remain approximately intermediate the extremities of itsslot 75.- As the take-up spool 15 and/or the drive wheel 21 operate,however, the length of ribbon 11 between them tends to vary as does theforce exerted by the ribbon on the roller. Specifically, as the take-upspool shortens the length of ribbon or as the drive wheel lengthens it,the roller 77 is pulled by the ribbon l1 and the spring 79, to thatphysical point in its path at which ribbon tension equals one-halfspring tension. If the spring 79 is chosen with a spring of constantelasticity such that contraction or expansion of the spring in theoperation of this apparatus is below the elastic limit, then the tensionon the ribbon 11 must also remain substantially constant since thespring counteracts all changes in ribbon tension.

. To insure that the spring 79 does not function outside the elasticlimit, the rotation of the take-up spool 15 is based on movement of theshunt; shunt movement, it will be remembered, corresponds to springmovement. As illustrated in FIGS. 4 and 5, a magnet 81 and a reed switch83 are disposed near and on opposite sides of the tapered end 69 of theshunt. The flux from magnet 81 affects the reed switch as influenced bythe tapered end of the shunt passing between the magnet and the switch.The contacts of the reed switch 83 are electrically' connected in serieswith a motor or other device which rotates shaft 27 to drive the take-upspool 15. As the roller 77 moves laterally, the tapered end 69 of themagnetic shunt is inserted further into or is further withdrawn from thespace between the magnet 81 and the switch 83. When the spring 79 iscompressed a predetermined maximum amount, within its constantelasticity range, the tapered shunt 69 is sufficiently withdrawn as tocorrespondingly increase the magnetic field and to maintain the switchcontacts closed and the take-up spool 15 rotating. As the spool 15takes-up used ribbon, ribbon tension increases, the spring 79 graduallyexpands and, at the same time, the tapered shunt 69 is inserted in themagnetic field of magnet 81. When the spring 79 has expanded apredetermined maximum amount, sufficient magnetic flux is diverted bythe tapered shunt 69 from the tension of the ribbon is reduced and theswitch contacts to allow them to open. Opening the contacts causes themotor (not shown) to cease rotating shaft 27 and spool 15. Thus ribbontake-up is stopped and this prevents further expansion of the spring 79.As the drive wheel 21 continues to feed ribbon 11 to the collectionapparatus 23 the spring 79 again contracts until the tapered shunt 69 issufficiently withdrawn from the magnetic field to allow sufficientmagnetic flux to affect and close the switch 83. The shaft 27 andtake-up spool are again rotated and the cycle repeats itself as long asthe drive wheel 21 continues to feed ribbon 11.

As shown in FIGS. 4 and 5, a second magnet 85 and reed switch 87 aremounted along the path of travel of the rectangular portion 67 of theshunt. The second switch and magnet are at the opposite end of the shunt67 from the tapered end 69. This second switch 87 is so positioned thatthe rectangular shunt portion 67 interrupts its magnetic field only inthe event that no ribbon or a broken ribbon is loaded in the system.This second switch and magnet also serve as a precautionary device toturn off the entire system in a similar fashion to that described forthe supply line tension mechanism switch 57 and shunt 55.

It should be noted that most efficient use of the substantially constantelastic range of the spring 79 may be obtained only if the reed switch83 reliably opens and closes at the same relative positions of taperedshunt 69 during repeated use. That is, permissive shunt travel must beaccurately controlled. This is best explained by reference to FIGS. 6Aand 6B in which a hypothetical shunt A includes only a rectangularportion 89 and shunt B includes a tapered portion 91 corresponding tothe shunt of the present invention. Conventional rectangular shunts suchas the type illustrated in FIG. 6A generally divert a relativelyconstant amount of flux over their length. That is, the flux density ata reed switch (not shown) will very nearly approach a maximum at alltimes when the shunt is withdrawn from the magnetic field and a minimumat all times when the shunt is inserted in the magnetic field. Theresponse time of the reed switch is thus a function of the time taken byits flexible contacts to react to the immediate change in a fluxdensity. This reaction time is not constant, and results in zones C(Close) and 0 (Open) along the shunt path during which the contacts mayclose and open, respectively. Opening or closing of the contacts mayoccur for any given shunt cycle at any point within the respective openor close zone. The width of the zones shown has been selected purely asa basis for this explanation.

Shunt B, such as is shown in FIG. 68 on the other hand, has a taperedextension 91 which enters the field at its narrow end and widens as theshunt is inserted further. As this shunt enters the field it diverts agradually increasing amount of flux from the switch contacts, andtherefore allows the resiliency of the contacts to predispose thecontacts toward an open position. When sufficient flux has been divertedthe predisposed contacts open, and the length of the zone of opening, 0,for shunt B is correspondingly smaller than that for shunt A due to thispredisposition. Similarly, on withdrawl of the shunt B from the field,the flux at the contacts is gradually increased and the contacts arepredisposed to close when sufficient closure flux is available.Consequently the length of the zone of closing C, for shunt B is alsosmaller than that for shunt A. if distance X, as shown in FIG. 6A, isassumed to be the distance the spring 79 may expand within its constantelastic range, then the maximum shunt travel must also be limited to thedistance X. Such a limitation on shunt A results in an appreciablysmaller minimum shunt travel, shown as A, than the same limitationapplied to shunt B which allows a minimum travel shown as B.Consequently the tapered shunt B offers two primary benefits in that itpermits maximum effective use of the constant elastic portion of spring79 expansion and also insures a maximum time between opening and closureof the reed switch 83, thereby increasing its cycle time. The decreasein switching operations and resulting minimization of energization andde-energization of the motor for the take-up spool 15 thereby result inappreciably longer life switch 83 and motor life. Optimization of theswitch and motor life is primarily a function of the tapered shunt whichis varied to suit a given application.

Since the ribbon 11 has been maintained at a constant vertical levelthroughout the system and the takeup spool 15 is at a higher level,guide means or level change means 25 is provided between the laststationary roller 63 and the take-up spool 15 to change ribbonelevation. Referring to FIG. 7 a rectangular plate 25 is mounted onframe 59 between the last roller 63 of the collection tension mechanism23 and the take-up spool 15. The width of the plate 25 (perpendicular tothe direction of ribbon travel) is greater than the width of the ribbon11 plus the radius of a full take-up spool 15. This latter requirementprevents the ribbon from slipping off the plate as the outer levels ofribbon are wound on spool 15. The height of the rectangular plate 25above the frame 59 is such that the ribbon 11, as it crosses therectangular plate 25, is at an elevation equal to the horizontal centerline 93 of the take-up spool 15. Therefore, as the ribbon 11 passes incontact with the upper edge of the rectangular plate 25 an even wrappingof ribbon about the take-up spool 15 is assured. In addition, the topedge of rectangular plate 25 provides a surface about which the ribbonmay be twisted 180 so that the inked surface of the ribbon will not beexposed as the ribbon is wrapped about the take-up spool 15.

Operation Now that the various elements of the system and the operationof the tapered shunt have been described in detail the operation of theentire system will be briefly summarized.

With the ribbon unwind and rewind system in an of condition ribbon 11passes from the supply spool 13 to the drive wheel 21 via the supplyline constant tension mechanism 17 and the printer 19. The ribbon 1 1 inthis portion of its path is under tension exerted by the roller 53. Fromthe drive wheel 21 the ribbon 11 passes to the take-up spool 15 via thecollection line tension mechanism 23. The ribbon 11 in this portion ofits path is under tension exerted by the biased roller 77. The taperedshunt 69 is fully inserted in the magnetic field of reed switch 83 andthe conventional take-up spool drive motor (not shown) is de-energized.

The drive wheel motor is energized by a ribbon demand circuit, notshown, which is related to the printer mechanism. The motor will remainenergized until the demand circuit returns to a non-demand state.

Initially, in the portion of the ribbon path between the supply spool 13and the drive wheel 21, energization of the drive wheel motor causes thedrive wheel 21 to pull ribbon 11 past the printer 19. As the ribbon ispulled, the tension mechanism roller 53 moves with lever 43 movingagainst spring 45 to release the necessary ribbon. Lever 43 rotates tothe point at which stud 49 engages the extremity of slot 47 in plate 35.Then, lever 43 and plate 35 rotate together releasing the brake orindentation 39 from sleeve 29. The supply spool 13 freely suppliesribbon 1 1 to the drive wheel 21 until roller 53, lever 43 and plate 35have returned to a position at which the brake 39 again engages thesupply reel sleeve 29 thus stopping rotation of the supply reel 13. Thisbraking and releasing of the supply reel 13 occurs cyclically while thesystem is operating. Should the ribbon 11 break at any time or should noribbon be loaded in the system, the lever 43 is rotated by spring 45causing the shunt to open the reed switch 87 which in turn shuts downthe entire system.

In the portion of the ribbon path between the drive wheel 21 and thetake-up spool 15, energization of the drive wheel 21 causes ribbon 11 tobe fed to the takeup spool 15. The roller 77 moves to maintainsubstantially constant tension on the ribbon 11 and simultaneouslywithdraws the tapered shunt 69 from the reed switch 83. As it iswithdrawn the magnetic flux around switch 83 gradually increases untilthe contacts close. Closure of the switch contacts completes the seriesconnected take-up spool motor circuit and the motor is energized. Thetake-up spool 15 collects ribbon 11, reversing the lateral motion of theroller 77 and reinserting the shunt 69 in the magnetic field of reedswitch 83. The flux affecting the switch 83 is gradually decreased untilthe contacts open, de-energizing the takeup spool motor and stoppingrotation of the take-up spool 15. This energization and de-energizationof the take-up reel motor occurs cyclically during energization of drivewheel 21. It should be noted that the intermittent operation of thetake-up spool 15 in conjunction with the substantially constant tensionmaintained on the ribbon 11 by the roller 77 effectively holds theribbon 1 1 on the take-up spool 15 within the upper tension limit of thespring 79. Should the ribbon 11 break at any time, should the ribbon onsupply spool come to an end (out of ribbon) or should no ribbon beloaded in the system, the shunt is urged to the right and opens thesecond reed switch 87 which in turn shuts down the entire system.

While both the supply 17 and take-up 23 tension mechanisms functioncyclically throughout the period of energization of the drive wheel 21,their cycles are entirely independent and the cycle time for each isdependent solely on its respective structural characteristics.

What is claimed is:

1. In a constant tension ribbon unwind and rewind apparatus includingribbon supply and takeup means, means for establishing a magnetic fluxfield, and means for driving said takeup means to rewind the ribbon theimprovement comprising:

means responsive to an increase in ribbon tension for unwinding ribbonfrom said supply means,

said unwinding means including brake means, first means for resilientlybiasing said brake means for stopping said unwinding of said ribbon, andan actuator coupled to said brake and having limited rotational freedom,said actuator being rotated by an increase in ribbon tension forcounteracting said brake bias,

second means for resiliently biasing said actuator for braking saidribbon unwinding,

switch means for controlling said driving means,

means resiliently biased in a first direction for closing said switchmeans and starting said driving means, and

said closing means being moved in a second direction by an increase inribbon tension for opening said switch means and stopping said drivingmeans.

2. The apparatus of claim 1 wherein:

said switch means is a magnetic flux responsive switch, and

said closing means includes a magnetic flux diverting member.

3. The apparatus of claim 2 wherein said magnetic flux diverting memberis tapered.

4. The apparatus of claim 1 wherein:

said brake means includes an elongated plate pivoted at one end thereofand having an arcuate slot at the other end thereof,

said actuator is pivoted at one end thereof in common with the pivot ofsaid brake means, and

said actuator further includes a projection for engaging the arcuateslot of said plate.

5. The apparatus of claim 1 wherein said ribbon supply means and saidribbon takeup means are coaxially aligned.

6. The apparatus of claim 1 wherein said ribbon takeup means includes:

a generally rectangular plate having at least one roller thereon, and

said plate being disposed adjacent to and slidably engaged with saidclosing means.

7. In apparatus for supplying ribbon to and unwinding ribbon from autilization device, the improvement for maintaining ribbon tensionwithin a predetermined range including:

a plurality of ribbon guiding elements collectively predisposed in acommon plane to form a sinuous transport path for a ribbon trained aboutthe elements,

a member having at least a portion thereof composed of magnetizablematerial shaped to form a tapered magnetic shunt,

means coupling one of said ribbon guiding elements to the member and forproviding limited joint displacement of the two in opposite directionsalong a prescribed path,

spring means yielding opposing displacement of the coupled element andmember in one direction along said prescribed path with a substantiallyconstant force,

means for varying the tension of a ribbon occupying said transport pathand being effective to displace the coupled element and member varyingdistances along said prescribed path but in the direction opposite tothat urged by the substantially constant force of said spring means,

a reed switch device including a magnet and a pair of magneticallyinfluenceable electrical contacts located within the normal range of themagnetic field of said magnet, said pair of contacts being capable ofassuming one or the other of two functional conditions depending on theflux density of the magnetic field applied by said magnet and in onecase assuming a circuit closed condition and in the other case a circuitopened condition, and

said reed switch device being located adjacent to the shunt portion ofsaid member and such that the tapered shunt is reversibly movable in'thespace between the magnet and the pair of electrical contacts in responseto the extent and direction of movement of the member caused byvariations in the tension of the ribbon by said ribbon tensioning means,the tapered formation of the shunt acting to gradually decrease the fluxdensity of the magnetic field applied to the pair of electrical contactsas the shuntis moved in the insertable direction relative to the spacebetween the electrical contacts and the magnet thus to cause thecontacts to assume one of said two functional conditions and togradually increase the fiux density of the magnetic field applied to thepair of electrical contacts as the shunt is moved in the withdrawaldirection relative to said space thus to cause the contacts to assumethe other of said two functional conditions.

8. In a tension dependent motor control system for advancing aribbon-like member along a transport path, the improvement including:

a motor driven shaft,

a ribbon supply spool and a ribbon take-up spool coaxially mounted onsaid drive shaft, the supply spool being journaled on the shaft forrotation relative thereto and the take-up spool being coupled to theshaft for joint rotation therewith,

a transport path leading from the supply spool and terminating at thetake-up spool, said transport path including a plurality of ribbonguiding elements collectively predisposed in a common plane and forminga sinuous portion of the transport path for a ribbon trained about theelements,

a member having at least a portion thereof composed of magnetizablematerial shaped to form a tapered magnetic shunt,

means coupling one of said ribbon guiding elements to the member and forproviding limited joint displacement of the two in opposite directionsalong a prescribed path,

means for varying the tension of a ribbon occupying said transport pathand causing displacements of the coupled element and member varyingdistances in one direction along said prescribed path in response tovariations in the tension of the ribbon,

spring means having a range of substantially constant elasticity and soconnected to the coupled element and member as to yieldingly opposetheir joint displacements along said prescribed path by said ribbontension varying means,

a reed switch device for controlling the operation of the motor drivenshaft including a magnet and a pair of magnetically influenceableelectrical contacts located within the normal range of the magneticfield of said magnet, said pair of contacts being capable of assumingone or the other of two functional conditions depending on the fluxdensity of the magnetic field applied by said magnet and in one caseclosing the circuit to the shafts motor and in the other case openingthe circuit to the shafts motor, and

said reed switch device being located adjacent to the shunt portion ofsaid member and such that the tapered shunt is reversibly movable in thespace between the magnet and the pair of electrical contacts in responseto the extent and direction of movement of the member by said ribbontension varying means, the tapered formation of the shunt cooperatingwith the range of constant elasticity of the spring means to increasethe time between the opening and closing of the contacts of the reedswitch device and acting to gradually decrease the flux density of themagnetic field applied to the electrical contacts when the shunt ismoved in the insertable direction relative to the space between thecontacts and the magnet thus to cause the contacts to assume one of saidtwo functional conditions and to gradually increase the flux density ofthe magnetic field applied to the electrical contacts when the shunt ismoved in the withdrawal direction relative to said space thus to causethe contacts to assume the other of said two functional conditions, theopening and closing of the circuit to the shafts motor resulting fromsaid two functional elasticity of the spring means.

1. In a constant tension ribbon unwind and rewind apparatus includingribbon supply and takeup means, means for establishing a magnetic fluxfield, and means for driving said takeup means to rewind the ribbon theimprovement comprising: means responsive to an increase in ribbontension for unwinding ribbon from said supply means, said unwindingmeans including brake means, first means for resiliently biasing saidbrake means for stopping said unwinding of said ribbon, and an actuatorcoupled to said brake and having limited rotational freedom, saidactuator being rotated by an increase in ribbon tension forcounteracting said brake bias, second means for resiliently biasing saidactuator for braking said ribbon unwinding, switch means for controllingsaid driving means, means resiliently biased in a first direction forclosing said switch means and starting said driving means, and saidclosing means being moved in a second direction by an increase in ribbontension for opening said switch means and stopping said driving means.2. The apparatus of claim 1 wherein: said switch means is a magneticflux responsive switch, and said closing means includes a magnetic fluxdiverting member.
 3. The apparatus of claim 2 wherein said magnetic fluxdiverting member is tapered.
 4. The apparatus of claim 1 wherein: saidbrake means includes an elongated plate pivoted at one end thereof andhaving an arcuate slot at the other end thereof, said actuator ispivoted at one end thereof in common with the pivot of said brake means,and said actuator further includes a projection for engaging the arcuateslot of said plate.
 5. The apparatus of claim 1 wherein said ribbonsupply means and said ribbon takeup means are coaxially aligned.
 6. Theapparatus of claim 1 wherein said ribbon takeup means includes: agenerally rectangular plate having at least one roller thereon, and saidplate being disposed adjacent to and slidably engaged with said closingmeans.
 7. In apparatus for supplying ribbon to and unwinding ribbon froma utilization device, the improvement for maintaining ribbon tensionwithin a predetermined range including: a plurality of ribbon guidingelements collectively predisposed in a common plane to form a sinuoustransport path for a ribbon trained about the elements, a member havingat least a portion thereof composed of magnetizable material shaped toform a tapered magnetic shunt, means coupling one of said ribbon guidingelements to the member and for providing limited joint displacement ofthe two in opposite directions along a prescribed path, spring meansyielding opposing displacement of the coupled element and member in onedirection along said prescribed path with a substantially constantforce, means for varying the tension of a ribbon occupying saidtransport path and being effective to displace the coupled element andmember varying distances along said prescribed path but in the directionopposite to that urged by the substantially constant force of saidspring means, a reed switch device including a magnet and a pair ofmagnetically influenceable electrical contacts located within the normalrange of the magnetic field of said magnet, said pair of contacts beingcapable of assuming one or the other of two functional conditionsdepending on the flux density of the magnetic field applied by saidmagnet and in one case assuming a circuit closed condition and in theother case a circuit opened condition, and said reed switch device beinglocated adjacent to the shunt portion of said member and such that thetapered shunt is reversibly movable in the space between the magnet andthe pair of electrical contacts in response to the extent and directionof movement of the member caused by variations in the tension of theribbon by said ribbon tensioning means, the tapered formation of theshunt acting to gradually decrease the flux density of the magneticfield applied to the pair of electrical contacts as the shunt is movedin the insertable direction relative to the space between the electricalcontacts and the magnet thus to cause the contacts to assume one of saidtwo functional conditions and to gradually increase the flux density ofthe magnetic field applied to the pair of electrical contacts as theshunt is moved in the withdrawal direction relative to said space thusto cause the contacts to assume the other of said two functionalconditions.
 8. In a tension dependent motor control system for advancinga ribbon-like member along a transport path, the improvement including:a motor driven shaft, a ribbon supply spool and a ribbon take-up spoolcoaxially mounted on said drive shaft, the supply spool being journaledon the shaft for rotation relative thereto and the take-up spool beingcoupled to the shaft for joint rotation therewith, a transport pathleading from the supply spool and terminating at the take-up spool, saidtransport path including a plurality of ribbon guiding elementscollectively predisposed in a common plane and forming a sinuous portionof the transport path for a ribbon trained about the elements, a memberhaving at least a portion thereof composed of magnetizable materialshaped to form a tapered magnetic shunt, means coupling one of saidribbon guiding elements to the member and for providing limited jointdisplacement of the two in opposite directions along a prescribed path,means for varying the tension of a ribbon occupying saId transport pathand causing displacements of the coupled element and member varyingdistances in one direction along said prescribed path in response tovariations in the tension of the ribbon, spring means having a range ofsubstantially constant elasticity and so connected to the coupledelement and member as to yieldingly oppose their joint displacementsalong said prescribed path by said ribbon tension varying means, a reedswitch device for controlling the operation of the motor driven shaftincluding a magnet and a pair of magnetically influenceable electricalcontacts located within the normal range of the magnetic field of saidmagnet, said pair of contacts being capable of assuming one or the otherof two functional conditions depending on the flux density of themagnetic field applied by said magnet and in one case closing thecircuit to the shaft''s motor and in the other case opening the circuitto the shaft''s motor, and said reed switch device being locatedadjacent to the shunt portion of said member and such that the taperedshunt is reversibly movable in the space between the magnet and the pairof electrical contacts in response to the extent and direction ofmovement of the member by said ribbon tension varying means, the taperedformation of the shunt cooperating with the range of constant elasticityof the spring means to increase the time between the opening and closingof the contacts of the reed switch device and acting to graduallydecrease the flux density of the magnetic field applied to theelectrical contacts when the shunt is moved in the insertable directionrelative to the space between the contacts and the magnet thus to causethe contacts to assume one of said two functional conditions and togradually increase the flux density of the magnetic field applied to theelectrical contacts when the shunt is moved in the withdrawal directionrelative to said space thus to cause the contacts to assume the other ofsaid two functional conditions, the opening and closing of the circuitto the shaft''s motor resulting from said two functional conditionsoccurring within the range of constant elasticity of the spring means.